Method for coating a component of an aircraft engine with a wear-resistant layer, and component for an aircraft engine with at least one wear-resistant layer

ABSTRACT

A method for coating a component of an aircraft engine with a wear-resistant layer, wherein the component is first coated at least regionally with a nickel- or cobalt-based alloy and subsequently aluminized. Also disclosed is a method for producing a spray powder for producing a wear-resistant layer of a component of an aircraft engine.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 of GermanPatent Application No. 102021127344.7, filed Oct. 21, 2021, the entiredisclosure of which is expressly incorporated by reference herein.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a method for coating a component of an aircraftengine with a wear-resistant layer, to a method for producing a spraypowder for producing a wear-resistant layer of a component of anaircraft engine, to a method for producing a wear-resistant layer on acomponent of an aircraft engine, to a component for an aircraft enginethat is provided at least regionally with a wear-resistant layer, and toan aircraft engine which comprises at least one such component.

2. Discussion of Background Information

Vibration and friction at contact points between components in aircraftengines cause wear. To protect the base material of the individualcomponents from this wear, thermally sprayed wear-resistant layers arefrequently applied. An example of a typical wear-resistant layer is athermally sprayed Tribaloy T800 layer. This layer, which can be used atup to 900° C., comprises a cobalt-based powder which is appliedtypically by high-velocity flame spraying (HVOF). It is likewise knownpractice to use nickel-based powders in order to produce such wearlayers.

The service temperatures of wear-resistant layers are limited due tooxidation at high temperatures. Where the layers are employed above thestated temperature of around 900° C., they suffer severe oxidation andprotection from wear is no longer provided for the base material of thecomponent. An attack on the base material leads subsequently topremature repair or to a need for the component to be replaced. Futureengine programs are aiming at ever higher temperatures in order toachieve the required efficiency. As a result of this, wear-resistantlayers are needed which can be employed reliably even at temperaturesabove 900° C.

In view of the foregoing, it would be advantageous to be able to providea method for coating a component of an aircraft engine with awear-resistant layer, a method for producing a spray powder forproducing a wear-resistant layer of a component of an aircraft engine, amethod for producing a wear-resistant layer on a component of anaircraft engine, a component for an aircraft engine that is provided atleast regionally with a wear-resistant layer, and an aircraft enginewhich comprises at least one such component, where the respectivewear-resistant layers can be employed reliably even at temperaturesabove 900° C.

SUMMARY OF THE INVENTION

The present invention provides a method for coating a component of anaircraft engine with a wear-resistant layer, a method for producing aspray powder for producing a wear-resistant layer of a component of anaircraft engine, a method for producing a wear-resistant layer on acomponent of an aircraft engine, a method for producing a wear-resistantlayer on a component of an aircraft engine, a component which isprovided at least regionally with a wear-resistant layer, and anaircraft engine which comprises one such component, each as set forth inthe independent claims. Advantageous embodiments with usefuldevelopments of the invention are specified in the respective dependentclaims; advantageous embodiments of each aspect of the invention aredeemed to be advantageous embodiments of the other aspects of theinvention.

A first aspect of the invention relates to a method for coating acomponent of an aircraft engine with a wear-resistant layer, wherein thecomponent is first coated at least regionally with a nickel- orcobalt-based alloy and subsequently aluminized. In other words, in theinvention, aluminum or an aluminum alloy is introduced subsequently intothe wear-resistant layer, and protects the wear-resistant layer fromoxidation by means of aluminum incorporated by diffusion. In the contextof the present disclosure, the term “aluminum” shall always be deemed toencompass “aluminum alloys” as well. Aluminizing in the context of thepresent disclosure refers to the accumulation of aluminum in thewear-resistant layer, which thereafter is better protected fromhigh-temperature oxidation and also against attack by other elements andcan therefore be operated reliably even at temperatures above 900° C.The accumulation of the aluminum may be only superficial or maypenetrate more deeply into the wear-resistant layer. At the extreme, thealuminum is present at least in substantially uniform distribution inthe wear-resistant layer. In general “a/an” in the context of thisdisclosure should be read as indefinite articles, i.e., always also as“at least one” unless expressly indicated otherwise. Conversely, “a/an”may also be understood as “only one”.

In one advantageous embodiment, the nickel- or cobalt-based alloy isaluminized by gas-phase aluminizing and/or by slip aluminizing and/orpowder pack aluminizing. In other words, the aluminum may be introducedinto the wear-resistant layer by way of a gas-phase operation, such aschemical vapor deposition (CVD), and/or by way of a slip process. As aresult, the wear-resistant layer can be aluminized optimally as afunction of the geometry and base material of the component.

In a further advantageous embodiment of the method of the invention, thewear-resistant layer after the aluminizing is subjected to heattreatment. This allows the distribution of the aluminum within thewear-resistant layer to be adjusted in a targeted way, since thealuminum diffuses into the interior of the wear-resistant layer as aresult of the heat treatment. It may further be assumed that in theoperation of the wear-resistant layer, at high temperatures in anaircraft engine, a relatively homogeneous distribution of the aluminumis established over time after a certain time. As a result of a targetedheat treatment, this condition can be produced from the outset, so thatthe properties of the wear-resistant layer in later operation are nolonger subject, at least substantially, to any change, even if at hightemperatures there is interdiffusion with the base material, which mayhave a different chemical composition than the wear-resistant layer. Theheat treatment may additionally cause alteration to the structure andthe microstructure of the wear-resistant layer. A heat treatment in thecontext of the present disclosure refers to a method for treating thecomponent provided with the wear-resistant layer, wherein at least thewear-resistant layer or the entire component is subjected to controlledheating and cooling again.

In a further advantageous embodiment of the invention, the heattreatment comprises diffusion annealing, which is especially suitablefor reducing microstructural inhomogeneities. Alternatively oradditionally it is provided that the heat treatment is carried out atpressure reduced relative to standard pressure and/or under protectivegas atmosphere. In this way it is possible in particular to control theoxygen content and to prevent unwanted oxidation.

Further advantages arise when the nickel- or cobalt-based alloy, afterapplication to the component and before the aluminizing, is at leastregionally nickel-plated. By means of preferably electrochemicalnickel-plating of the wear-resistant layer, the diffusion of thealuminum into the layer can be promoted. In the case of nickel-basedalloys, this step is frequently not necessary, but is neverthelessuseful in certain cases.

In a further advantageous embodiment of the invention, the nickel- orcobalt-based alloy is selected from CoMoCrSi alloys, more particularlyT800, NiMoCrSi alloys, and CoCrWNi alloys. This allows the advantages ofthe wear-resistant layer produced in accordance with the invention to berealized for alloys that are commonplace and established in engineconstruction.

In one embodiment of the invention the nickel- or cobalt-based alloy isCoMoCrSi alloy, namely T800, with 27-30 wt % Mo, 16.5-18.5 wt % Cr,3-3.8 wt % Si, and the balance Co and unavoidable impurities. Theseunavoidable impurities may comprise up to 1.7 wt % per constituent, upto 3.5 wt % in total, and/or may comprise the constituents Fe, Ni, O, C,P, and S. The Mo constituent in this case may introduce hardness andtribooxides for advantageous wear protection.

In one embodiment of the invention the nickel- or cobalt-based alloy isa NiMoCrSi alloy, namely T700, with 31-34 wt % Mo, 14.5-16.5 wt % Cr,3-3.8 wt % Si, and the balance Ni and unavoidable impurities. Theseunavoidable impurities may comprise up to 3.2 wt % per constituent, upto 4.1 wt % in total, and/or may comprise the constituents Fe, Co, O, C,P, and S. The Mo constituent in this case may introduce hardness andtribooxide for advantageous wear protection.

In one embodiment of the invention the nickel- or cobalt-based alloy isa CoCrWNi alloy, with 24.5-26.5 wt % Cr, 6.5-8.0 wt % W, 9.5-11.5 wt %Ni, 0-0.6 wt % C, more particularly 0.42-0.55 wt % C, and the balance Coand unavoidable impurities. These unavoidable impurities may comprise upto 2.2 wt % per constituent, up to 4.5 wt % in total, and/or maycomprise the constituents Fe, Mn, Si, P, and S. The W constituent inthis case may introduce hardness for advantageous wear protection.

A second aspect of the invention relates to a method for producing spraypowder for producing a wear-resistant layer of a component of anaircraft engine, wherein a nickel- or cobalt alloy is provided, admixedwith aluminum and/or an aluminum alloy, and jointly melted and/oratomized. This represents an advantageous possibility for providing aspray powder which is suitable for producing a temperature-stable andoxidation-resistant wear-resistant layer comprising analuminum-containing or aluminized nickel- or cobalt-based alloy. Thejoint atomization and/or melting ensures that the aluminum is present inrelatively uniform distribution in the powder from the outset, meaningthat a wear-resistant layer produced using the spray powder likewise hasa relatively uniform distribution of aluminum from the outset. Furtherfeatures and their advantages are apparent from the descriptions of thefirst aspect of the invention.

A third aspect of the invention relates to a method for producing awear-resistant layer on a component of an aircraft engine, wherein afirst powder composed of a nickel- or cobalt-based alloy is mixed with asecond powder composed of aluminum and/or aluminum alloy, after whichthe first and second powders are thermally sprayed at least onto aregion of the component, in order to produce the wear-resistant layer.This represents a further advantageous alternative for the production ofa temperature-stable and oxidation-resistant wear-resistant layercomposed of an aluminum-containing or aluminized nickel- or cobalt-basedalloy. The first and second powders are preferably sprayedsimultaneously if homogeneous mixing is desired. Alternatively the firstand second powders may be sprayed successively or in temporally varyingproportions in order to achieve a defined aluminum distribution in thewear-resistant layer. Further features and their advantages are apparentfrom the descriptions of the preceding aspects of the invention.

A fourth aspect of the invention relates to a method for producing awear-resistant layer on a component of an aircraft engine, wherein acomposite powder composed of a first powder which consists of a nickel-or cobalt-based alloy and of a second powder which consists of aluminumand/or aluminum alloy is produced, after which the composite powder isthermally sprayed at least onto a region of the component, in order toproduce the wear-resistant layer. This represents a further advantageousalternative for producing a temperature-stable and oxidation-resistantwear-resistant layer composed of an aluminum-containing or aluminizednickel- or cobalt-based alloy. The composite powder may consistgenerally of loose and/or mutually adhered powder particles. Rather thanthe use of two different powders, a composite powder is used which issprayed as one component, in order to produce the aluminizedwear-resistant layer. In this way, particularly uniform distribution ofthe aluminum in the wear-resistant layer can be ensured. Furtherfeatures and their advantages are apparent from the descriptions of thepreceding aspects of the invention.

A fifth aspect of the invention relates to a component for an aircraftengine, provided at least regionally with a wear-resistant layer. Inaccordance with the invention the wear-resistant layer consists of analuminized nickel- or cobalt-based alloy. The wear-resistant layerallows the component to be used reliably in an aircraft engine even attemperatures above 900° C. Further features and their advantages areapparent from the descriptions of the preceding aspects of theinvention.

A sixth aspect of the invention relates to an aircraft engine whichcomprises at least one component according to the fifth aspect of theinvention and/or which comprises at least one component that has awear-resistant layer which is produced in accordance with the firstaspect of the invention and/or which is generated from a spray powderproduced in accordance with the second aspect of the invention and/orwhich is produced by means of a method according to the third or fourthaspects of the invention. This allows the component to be used reliablyin the aircraft engine even at temperatures above 900° C., endowing theaircraft engine with enhanced efficiency. Further features and theiradvantages are apparent from the descriptions of the preceding aspectsof the invention.

Further features of the invention are apparent from the claims, theFIGURES, and the description of the figures. The features and featurecombinations stated above in the description, and also the features andfeature combinations stated hereinafter in the description of theFIGURES, and/or shown alone in the FIGURE, can be used not only in theparticular combination indicated, but also in other combinations,without departing the scope of the invention. It is therefore the casethat the invention is also deemed to encompass and disclose embodimentswhich are not explicitly shown and elucidated in the FIGURE, arenevertheless consequent upon and can be generated by separate featurecombinations from the embodiments elucidated. Also considered to bedisclosed are embodiments and feature combinations which, accordingly,do not have all of the features of an originally formulated independentclaim. The disclosure is additionally deemed to encompass embodimentsand feature combinations, especially by virtue of the embodiments setout above, which go beyond or deviate from the feature combinations setout in the dependency references of the claims. The single FIGURE showsa diagram of the distribution of aluminum in a wear-resistant layer of acomponent of an aircraft engine as a result of diffusion at differenttimes.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing,

the only FIGURE is a diagram showing the concentration of aluminum C inwear-resistant layer as a function of the distance A from an interfaceat different times t.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the FIGURE, the concentration of aluminum C is shown on the y-axis asa function of, on the x-axis, a distance A from an interface, markedwith “0”, of a wear-resistant layer composed of a nickel- orcobalt-based alloy of a component of an aircraft engine, at threedifferent times t₁, t₂, and t₃. To the left of the interface of theoriginal wear-resistant layer, marked with 0, is the aluminizing layer Sgenerated in each case, while the wear-resistant layer extends to theright of the layer surface marked with 0.

According to the present state of the art, Ni- or Co-basedwear-resistant layers cannot be used stably above 900° C. owing to theircomposition. The reason for this is the failure of the layer byoxidation at high temperatures. The present invention is based on thefinding that aluminum as protection from temperature and oxidation canbe introduced by diffusion into typical Ni- or Co-based wear-resistantlayers, allowing the resultant aluminized wear-resistant layers to beoperated reliably even above 900° C. It is intended preferably that thewear-resistant layers may be produced by thermal spraying.

The possibility of producing a high-temperature wear-resistant layer, bydiffusion of aluminum as protection from oxidation into existingwear-resistant layers, was demonstrated in the following experiments. Atotal of three different wear-resistant layers, based on Co (forexample, CoMoCrSi) or based on Ni (for example NiMoCrSi) were producedby thermal spraying on a component of an aircraft engine, andsubsequently aluminized. In certain experiments, the aluminum wasintroduced into the respective wear-resistant layer by gas-phasealuminizing, and in other experiments via a slip route. Some of thecoated components were subsequently heat-treated under reduced pressure.

The wear-resistant layers were each evaluated metallographically.Moreover, after the gas-phase aluminizing and also after the subsequentreduced-pressure heat treatment, elemental analysis (EDX) was carriedout on a polished section in order to understand how far the aluminum isdiffused into the wear-resistant layers.

1. Gas-Phase Aluminizing

After the gas-phase aluminizing (CVD), aluminum incorporated bydiffusion was detected both in the Ni-based wear-resistant layer and inthe two Co-based wear-resistant layers. The Al content is highest at thelayer surface and decreases with increasing distance A from the surfaceof the wear-resistant layer. This behavior is typical of diffusionlayers. For this reason, subsequent to the gas-phase aluminizing, anadditional diffusion anneal was carried out under reduced pressure, inorder to achieve a more uniform distribution of the Al content over thelayer thickness A of the wear-resistant layers. The evaluation of theelemental analysis (EDX) after the diffusion anneal is represented inthe FIGURE. The aluminum content C of the layer surface of thealuminizing S drops after the heat treatment (dashed line t₂);conversely, the aluminum is detectable at a greater distance from thelayer surface in comparison to the wear-resistant layer after thealuminizing (dotted line t₁). After this heat treatment as well, whichwas carried out at the same temperature as the aluminizing, there isstill no homogeneous distribution of the aluminum over the layerthickness A. The temperature may be, for example, between 750° C. and900° C. or more. By prolonging the heat treatment and/or by thetemperatures during operation of the component in an aircraft engine,the aluminum diffuses further and is uniformly distributed in thewear-resistant layer, producing a uniform distribution of the Alconcentration C over the thickness of the wear-resistant layer. This isrepresented schematically with the distribution curve t₃.

2. Slip Aluminizing

After the application of the Al-containing slip, it isdiffusion-annealed by a heat treatment in protective gas. Thetemperature with this kind of aluminizing is lower by comparison withthe gas-phase aluminizing. After the diffusion anneal, all of thewear-resistant layers exhibit a marked laminarity, consisting of adeposited layer, a diffusion zone, and a zone in which the lamellarthermal spray layer is still clearly apparent. The deposited layersproduced differ significantly between the Co- and Ni-based layers. Whilein the case of Ni-based layer a dense deposited layer is formed, thelayer in the case of the two Co-based layers is interdisposed withpores.

During the introduction of aluminum into the wear-resistant layer, careshould be taken to ensure that the actual function of protection fromwear is maintained. This means that, after the aluminizing of the layer,the hardness must be similar and the required wear resistance must beensured. Too high or too low an Al content ought therefore to begenerally avoided.

It has been shown that aluminum can be introduced into thermally sprayedwear-resistant layers by diffusion. Not only aluminized wear-resistantlayers composed of Ni-based alloys but also those composed of Co-basedalloys have been produced. In general it is possible for not only theNi- or Co-based alloys stated above but instead all such alloys to bealuminized in the manner described.

Depending on the method, nature, and duration of a subsequent heattreatment, a high concentration of the aluminum is produced on thesurface of the wear-resistant layer, the concentration decreasing to agreater or lesser extent with the distance A from the surface layer,depending on layer composition. It has been possible to show that thedistribution of the aluminum can be adapted by subsequent heat treatmentand hence by further diffusion of the aluminum. It may also be assumedthat in the operation of the wear-resistant layer, at high temperaturesand after a certain time, a homogeneous or at least quasi-homogeneousdistribution of the aluminum comes about over time (t₃).

Through the selection of the appropriate aluminizing method and throughoptimization of parameters, it is possible for each component togenerate an optimal wear-resistant layer which exhibits an even oruneven profile in the aluminum concentration C, starting from the layersurface. The profile in the aluminum concentration C may even out aftera certain time as a result of further diffusion in the operation of thecomponent.

In order to achieve a homogeneous distribution of the aluminum over thelayer thickness of the wear-resistant layer from the start, provisionmay be made to admix the Co- or Ni-based powder with aluminum powderbefore the thermal spraying. In the case of uniform mixing of thepowder, the distribution of the aluminum in the layer assembly isconsequently homogeneous or at least largely homogeneous directly afterthe thermal spraying. In the event of any difficulties caused byseparation in the case of this technique, alternative provision may bemade for the Co- or Ni-based powder to be adhered with Al powder. Thecomposite powder produced in this way would likewise lead to homogeneousor at least largely homogeneous Al distribution in the resultantwear-resistant layer.

A further technique is that of admixing aluminum to the initial Ni- orCo-alloy from which the powder for the wear-resistant layer is produced.In this case, following atomization, the spray powder already has thedesired Al content. With this variant, moreover, there is no likelihoodof unwanted separation of the aluminum or powder separation.

The parameter values indicated in the documents for the definition ofoperating and measuring conditions for the characterization of specificproperties of the subject matter of the invention are also deemed to beencompassed in the scope of the invention within the bounds ofdeviations—arising, for example, from measurement errors, systemicerrors, weighing errors, DIN tolerances, and the like.

LIST OF REFERENCE SYMBOLS

-   C concentration of aluminum-   A distance from an interface of a wear-resistant layer-   0 interface of the wear-resistant layer-   S aluminizing-   t₁-t₃ heat treatment timepoints

What is claimed is:
 1. A method for coating a component of an aircraftengine with a wear-resistant layer, wherein the method comprises (i)first coating the component at least regionally with a nickel- orcobalt-based alloy and subsequently aluminizing the thus coatedcomponent, or (ii) mixing a first powder of a nickel- or cobalt-basedalloy with a second powder of aluminum and/or aluminum alloy, followedby thermally spraying the first and second powders at least onto aregion of the component, in order to produce the wear-resistant layer,or (iii) producing a composite powder composed of a first powderconsisting of a nickel- or cobalt-based alloy and of a second powderconsisting of aluminum and/or an aluminum alloy, followed by thermallyspraying the composite powder at least onto a region of the component,in order to produce the wear-resistant layer.
 2. The method of claim 1,wherein in (i) the nickel- or cobalt-based alloy is aluminized bygas-phase aluminizing and/or by slip aluminizing and/or by powder packaluminizing.
 3. The method of claim 1, wherein in (i) the nickel- orcobalt-based alloy is aluminized by gas-phase aluminizing.
 4. The methodof claim 1, wherein in (i) the nickel- or cobalt-based alloy isaluminized by slip aluminizing.
 5. The method of claim 1, wherein in (i)the nickel- or cobalt-based alloy is aluminized by powder packaluminizing.
 6. The method of claim 1, wherein in (i) the wear-resistantlayer after aluminizing is subjected to a heat treatment.
 7. The methodof claim 6, wherein the heat treatment comprises diffusion annealingand/or is carried out at a reduced pressure relative to standardpressure and/or under a protective gas atmosphere.
 8. The method ofclaim 1, wherein in (i) the nickel- or cobalt-based alloy, afterapplication to the component and before aluminizing, is at leastregionally nickel-plated.
 9. The method of claim 1, wherein the nickel-or cobalt-based alloy is selected from CoMoCrSi alloys, NiMoCrSi alloys,and CoCrWNi alloys.
 10. The method of claim 1, wherein the nickel- orcobalt-based alloy comprises a CoMoCrSi alloy, namely T800 having thefollowing composition: Mo: 27-30 wt %, Cr: 16.5-18.5 wt % Si: 3-3.8 wt %

balance Co and unavoidable impurities.
 11. The method of claim 1,wherein the nickel- or cobalt-based alloy comprises a NiMoCrSi alloy,namely T700 having following composition: Mo: 31-34 wt %, Cr: 14.5-16.5wt %, Si: 3-3.8 wt %,

balance Ni and unavoidable impurities;
 12. The method of claim 1,wherein the nickel- or cobalt-based alloy comprises a CoCrWNi alloy withfollowing composition: Cr: 24.5-26.5 wt %, W:  6.5-8.0 wt %, Ni: 9.5-11.5 wt %, C: 0-0.6 wt %, in particular 0.42-0.55 wt %,

balance Co and unavoidable impurities.
 13. The method of claim 1,wherein the method comprises (i).
 14. The method of claim 1, wherein themethod comprises (ii).
 15. The method of claim 1, wherein the methodcomprises (iii).
 16. A method for producing a spray powder for producinga wear-resistant layer of a component of an aircraft engine, wherein themethod comprises admixing a nickel- or cobalt-based alloy with aluminumand/or an aluminum alloy, and jointly melting and/or atomizing aresultant mixture.
 17. A component for an aircraft engine, wherein thecomponent is provided at least regionally with a wear-resistant layer,the wear-resistant layer comprising an aluminized nickel- orcobalt-based alloy.
 18. The component of claim 17, wherein the componenthas been produced by a method which comprises first coating thecomponent at least regionally with a nickel- or cobalt-based alloy andsubsequently aluminizing the thus coated component.
 19. An aircraftengine which comprises at least one component according to claim 17.